1. Field of the Invention
The invention relates printing machines, and more particularly, to a double printing unit of a rotary printing machine which can be switched off for a rapid production change, while the web continues to be led through between the transfer cylinders which have been moved out of contact.
2. Description of the Related Art
DE 93 11 113 U1 shows a double printing unit serving as a single printing unit, in which the form and transfer cylinders are arranged one above another. All four printing-unit cylinders have a drive connection to spur gears located on their journals. The drive is provided by means of a main shaft via a bevel-gear mechanism and an intermediate gear on one of the spur gears of the transfer cylinders. This drive can be disengaged by means of a clutch when the double printing unit is switched off for a plate change needed in the event of a production change. In order to put the drive back into service, the double printing unit is accelerated by means of an auxiliary drive, then coupled to the main shaft and finally printing is thrown on.
In the case of the single printing unit, the transfer cylinders have to be thrown relatively far off in the thrown-off state in order to lead the web which is printed, or is to be printed, by other printing units horizontally through between the transfer cylinders without contact. However, in order to prevent the spur wheels from being disengaged, limits are placed on the extent of the spacing. It is also necessary for there to be sufficient tooth engagement in order to accelerate a double printing unit of this type before printing is switched on in the event of a production change. Guide rolls are therefore provided upstream and downstream of the double printing unit. The guide rolls aid in the leading of the web through and between the transfer cylinders spaced apart from one another. The guide rolls make the double printing unit costly. Furthermore, ink is deposited on them, and, in a reverse action, is smeared on the web again.
According to Swiss Patent 549 471, the transfer cylinders of a double printing unit are each mounted in levers which can be pivoted around the associated form cylinder. The form and transfer cylinders and the transfer cylinders have a mechanical drive connection via spur gears on their journals. For the purpose of throwing off the printing, the levers, together with the transfer cylinders, are pivoted by means of toggle levers acting on the journals of the transfer cylinders. When such a double printing unit is used as a single printing unit, again the transfer cylinders have to be thrown off relatively far, in order to make it possible to lead through the web printed or to be printed by other printing units in this thrown-off state. However, the aforementioned limits are placed on the extent of the spacing, in order to prevent the transfer cylinders from being disengaged and, in addition, there is still sufficient tooth engagement in order to stop and accelerate the switched-off double printing unit.
U.S. Pat. No. 4,458,590 shows a double printing unit with printing-unit cylinders arranged one above another, which are all mounted in side walls by means of eccentric bushes. Here, too, limits are placed on the throw-off distances of the transfer cylinders, in order that engagement conditions which are still sufficiently good are provided for the spur gears in the thrown-off state.